This invention relates to a monitor of pressure intervals with control capabilities that can provide data obtained from either the detection of very low positive, negative or differential pressures that can be used to control devices having uses in health care and industry.
Originally the primary purpose was to develop a sensor that could detect the very low negative pressure occurring at the nasal passageways, in order to monitor respiration.
A simple way was developed for doing this and U.S. Pat. No. 4,878,502, Nov. 7, 1989, was issued. This sensor consisted of a very low density ball moving in a transparent tube with its position being optically sensed. However, due to the very low density of the ball, it was attracted by static and the forces of cohesion to stick to the tube. To eliminate this sticking to the tube it was necessary to coat the ball with graphite. The graphite created a conductive coating to prevent the static attraction, but its main purpose was to put a coating on the ball that prevented the very few electrons in the low density ball being attracted to the much denser electrons in the plastic tube by the forces of cohesion.
This made possible an inexpensive device that could detect when apnea occurred (failure to breath for 10 seconds or longer) and was suitable for use as a monitor for possible prevention of crib-death (SIDS). However, in use it was best if a filter was used to prevent the possibility of the graphite powder being ingested. This reduced the sensitivity and with the fact that the ball could last for approximately 100,000 operations (when it would require refurbishing) it was not too suitable for health care use. The device was found to be better suited for industrial use. Its industrial use is to detect airflow (example: act as a safety interlock switch to detect loss of airflow in air cooled electronic equipment) and other uses such as to detect the low pressure maintained in clean rooms to prevent the entrance of contaminated air. In industrial applications where the equipment had the switch working only when the equipment was turned on or off once a day, a life of 10,000 operations would be the normal requirement and the 100,000 operations of the plastic ball's operating life was extremely satisfactory. A filter is not required for industrial applications so the sensitivity is high.
When the previous device was used for detecting apnea in infants to prevent crib-death (SIDS), it was necessary for the device to be connected to the infant's nasal cavities by the use of a nasal cannula normally used for administering oxygen.
A simpler way was developed so it would not be necessary to subject the baby to wearing a nasal cannula. This simpler way was for the baby to wear the pneumatic breathing belt sensor with minimum space maintaining tapes, U.S. Pat. No. 4,602,643--Jul. 29, 1986. The use of the belt overcame the requirement that a filter be used, and it, therefore, made it possible to use the maximum sensitivity of the ball type sensor.
The limited number of operations of the ball type sensor required that a more satisfactory sensor, with a longer operating life, be developed. This resulted in a sensor employing a diaphragm being created that detected the movement of the diaphragm by the use of optoelectronics. This device had excellent sensitivity and U.S. Pat. No. 4,745,925, May 24, 1988, was issued for this device. This device not only sensed the low negative pressure of inhalation, but eliminated the need for a filter, and had a life of over 10 million operations. The patent also described its use for inhalation therapy, where each time a breath is taken it triggers a dose of oxygen. The dose of oxygen was for a fixed period of time, adjusted manually. The use of intermittent flow of oxygen over the normal continuous flow can result in 50 to 70% savings in the cost of oxygen. This is possible since a human inhales approximately 30% of the time and exhales 70% of the time; 30% of the oxygen goes into the patient and the other 70% goes into the room and is wasted.
It was found that this unit operated satisfactorily in the day time when the patient was breathing through his nose. However, during sleep the patient could breath through his mouth and this reduced the negative pressure so much at the nasal cavities that it could not be sensed by the optoelectronic sensor.
This led to a development of a mouth nose mask, U.S. Pat. No. 5,005,517--Apr. 9, 1991, that provided for diversion of some of the oral inhalation air to the nasal passageways where it could be sensed by a nasal cannula connected to the monitor employing the optoelectronic sensor.
U.S. Pat. No. 5,024,219--Jun. 18, 1991 shows how the above developed unit, U.S. Pat. No. 4,745,925--May 24, 1988, can have multiple uses such as being used from four possible sources of supply; a large tank of breathable gas, a small tank of breathable gas, a wall outlet supplied from a bulk storage system of breathable gas, and an oxygen concentrator supplying oxygen from ambient air.
All of the above used a fixed dose of oxygen that had to be manually adjusted, U.S. Pat. No. 5,038,771--Aug. 13, 1991 was issued for a new developed method where the dose of oxygen was determined by taking a percentage of a previous breath, thus automatically adjusting to a rate of breathing of air-breathing animals, including humans.
In an effort to create a sensor that could be manufactured at lower cost, a capacitance sensor, U.S. Pat. No. 5,052,400--Oct. 1, 1991 was developed.
Further development made it possible for a single monitor to sense respiration by use of a nasal cannula or a pneumatic breathing belt. This made it possible for the best method to be selected, at the bedside, for utmost patient comfort, and for which U.S. Pat. No. 5,074,299--Dec. 24, 1991 was issued.
The experience gained from the development of the above products resulted in an effort to develop a device that would have greater sensitivity, lower cost, unlimited control capabilities, longer life, smaller size, and the ability to be programmed to the special requirements of an unlimited number of applications. This resulted in the development of the monitor for low pressure intervals with control capabilities as explained in the summary of this invention, that can do all the past functions and many new sophisticated functions because it is software controlled. It also employs a newly developed vane type sensor that is more sensitive, smaller size, and less costly to manufacture.
When used as a medical device for inhalation therapy, it provides for an intermittent flow of oxygen to save cost while being clinically equivalent to continuous flow now in use. It also provides for a higher quality health care because it can signal if the patient is not receiving the benefit of the therapy.